A heat sink for absorbing heat which is generated by an electronic module by using a coolant which flows in its internal portion, comprises a housing which is provided with, in its internal portion, a first surface which is located in the vicinity of the electronic module and a second surface which faces the first surface and comprises fins which extend from the first surface toward the second surface, wherein a projecting portion projecting from the second surface toward the first surface is formed at the second surface, between the top edges of the fins on the second surface side and the second surface.